1. Field of the Invention
The present invention relates to the field of optical recording media, and more particularly, to a disc having spare areas for defect management, and an apparatus for allocating and assigning spare areas and for handling fragmented ECC blocks.
2. Description of the Related Art
In order to manage defects on a general recordable/rewritable disc, slipping replacement for skipping defects without providing logical sector numbers to the defects, is used for defects (primary defects) generated upon initialization of the disc, and linear replacement for replacing error correction code (ECC) blocks of an erroneous zone with normal blocks in a spare area, is used for defects (secondary defects) generated during use of the disc.
That is, slipping replacement is used to minimize a reduction in the recording or reproduction speed due to defects, in which a logical sector number to be provided to a sector which is determined to be defective during a certification process for inspecting defects of a disc when the disc is initialized, is provided to a sector next to the defective sector, that is, data is recorded or reproduced by slipping a sector where a defect is generated during recording or reproduction. Here, an actual physical sector number is shifted by the sector number designated by skipping the defective sector. Such a shifting-backwards phenomenon is solved by using as many sectors as there are defects in a spare area located at the end portion of a corresponding recording area (group or zone). According to the specifications, the position of a defective sector replaced by slipping replacement is prescribed to be recorded in a primary defect list (PDL) in a defect management area (DMA) on a disc.
Slipping replacement cannot be used for a defect which is generated while a disc is being used. When a defective portion is disregarded or skipped, discontinuity is introduced into the logical sector numbering, which means that slipping replacement violates file system rules. Thus, linear replacement is used for defects generated during use of the disc, in which an ECC block including a defective sector is replaced by an ECC block existing in a spare area. The location of the defective block replaced by linear replacement is prescribed to be recorded in a secondary defect list (SDL) in a defect management area on a disc. When linear replacement is used, logical sector numbering is not interrupted. However, when there is a defect, the positions of sectors on a disc are discontinuous, and real data for a defective ECC block exists in a spare area.
Meanwhile, a digital versatile disc random access memory (DVD-RAM) according to the DVD-RAM standard version 1.0 is comprised of a plurality of groups each having a user area and a spare area which are constant in each zone. FIG. 1A is a half plan view of a disc showing a user area a guard area and spare area, and FIG. 1B one-dimensionally shows several zones on a disc. Each zone is comprised of a guard area, a user area, a spare area, and a guard area which are sequentially arranged.
A disc is segmented into zones to solve inaccurate recording due to a change in the speed of a spindle during recording and to use a zone constant linear velocity (ZCLV) method in order to increase the search speed with respect to a constant linear velocity method.
That is, when defects are managed by the linear replacement, if possible, linear replacement within a defective zone increases the search speed since there is no change in the linear velocity of a disc. Thus, the DVD-RAM allocates a certain amount of spare area to each zone as shown in FIG. 1B, to accomplish linear replacement.
In this existing defect management method, each zone acts as a group, and a spare area is allocated at the end of each group. Each group is managed as a defect management area. Also, since the start sector number of each group is predetermined, an ECC block is supposed to start at the start position of a zone which is a unit for physically segmenting an area.
The start logical sector number of each group is designated as described above. Thus, when defects are managed by slipping replacement, slipping replacement must be performed only within a corresponding group. In order to replace defects generated in a corresponding group using the slipping replacement, the number of defective sectors that are slipped must be less than the number of usable sectors in a spare area in the corresponding group. Accordingly, a restriction that a large defect generated in one group must be processed within the group limits the maximum size of a defect that can be replaced by the slipping replacement.
If the size of defects to be replaced by slipping replacement is greater than the size of a spare area in a corresponding group, a spare area in another group must be used by linear replacement. However, when linear replacement is used, defects are managed not in units of sectors but in units of ECC blocks, that is, in units of 16 sectors. Thus, a spare area of 16 sectors is required to process one defective sector, which degrades the efficiency of defect management.
Also, a standard size of a spare area for defect management is predetermined, so that spare areas of the same size must be also allocated in applications to which defect management using linear replacement cannot be applied, such as real time recording. Therefore, the efficiency of area utilization of a disc is degraded.